When the liquid being pumped enters the eye
of a centrifugal pump, the pressure is significantly reduced.
The greater the flow velocity through the pump the greater
this pressure drop. If the pressure
drop is great enough, or if the temperature of the liquid is
high enough, the pressure drop
may be sufficient to cause the liquid to flash to steam when
the local pressure falls below the
saturation pressure for the fluid that is being pumped. These
vapor bubbles are swept along the
pump impeller with the fluid. As the flow velocity decreases
the fluid pressure increases. This
causes the vapor bubbles to suddenly collapse on the outer
portions of the impeller. The formation
of these vapor bubbles and their subsequent collapse is cavitation.
Cavitation can be a very serious problem for
centrifugal pumps. Some pumps can be designed to
operate with limited amounts of cavitation. Most centrifugal
pumps cannot withstand cavitation
for significant periods of time; they are damaged by erosion
of the impeller, vibration, or
some other cavitation-induced problem.
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